Über die kinetik des thermischen abbaues von polystyrolen

Caşcaval, Von C. N.; Vasile, Cornelia; Schneider, I. A.

doi:10.1002/macp.1970.021310105

Cited by 15 publications

(4 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A significant increase in total volatile yield was found for most of the coals tested if the heating rate was increased from 1 to 1000 K/s. An effect of the heating rate was also reported by some authors for polymers (see, for instance, Cascaval et al, 1970).…”

Section: Influence Of the Heating Rate In The Screensupporting

confidence: 73%

Examination and Evaluation of the Use of Screen Heaters for the Measurement of the High Temperature Pyrolysis Kinetics of Polyethene and Polypropene

Westerhout

Balk

Meijer

et al. 1997

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

A screen heater with a gas sweep was developed and applied to study the pyrolysis kinetics of low density polyethene (LDPE) and polypropene (PP) at temperatures ranging from 450 to 530°C. The aim of this study was to examine the applicability of screen heaters to measure these kinetics. On-line measurement of the rate of volatiles formation using a hydrocarbon analyzer was applied to enable the determination of the conversion rate over the entire conversion range on the basis of a single experiment. Another important feature of the screen heater used in this study is the possibility to measure pyrolysis kinetics under nearly isothermal conditions. The influence of the mixing process in the gas phase on the measured hydrocarbon concentration versus time curve was assessed and it was demonstrated that the residence time distribution of the gas phase, which has to be accounted for to correctly interpret the experiments, becomes the limiting factor when measuring pyrolysis kinetics at high temperatures and not the heat transfer rate. With this type of apparatus, pyrolysis reactions with a first order rate constant lower than 2 s -1 can be studied, which implies that the pyrolysis kinetics of the forementioned polymers could be determined at temperatures below 530°C. The kinetic constants for LDPE and PP pyrolysis were determined, using a first order model to describe the conversion rate in the 70-90% conversion range and the random chain dissociation model for the entire conversion range. Our experiments revealed that both LDPE and PP posses the same conversion rate, which is unexpected behavior since PP should be more sensitive to thermal degradation than LDPE. A comparison of the thermo gravimetric analyzer results with those obtained with the screen heater indicates an enhancement of the pyrolysis kinetics in the latter equipment. Several hypothesis were tested to explain this phenomenon and led to the suspicion that the discrepancy is possibly due to the effect of the electrical current passing through the screen on the pyrolysis reaction, although most of the evidence for this hypothesis is indirect. Screen heaters can therefore not be used in this configuration to measure the pyrolysis kinetics, if this hypothesis is correct. In addition to the experimental work two single particle models have been developed which both incorporate a mass and a (coupled) enthalpy balance, which were used to assess the influence of internal and external heat transfer processes on the pyrolysis process. The first model assumes a variable density and constant volume during the pyrolysis process, whereas the second model assumes a constant density and a variable volume. An important feature of these models is that they can accommodate kinetic models for which no analytical representation of the pyrolysis kinetics is available. Model calculations revealed that heat transfer limitations were not important during the pyrolysis experiments performed in the screen heater and could not explain the forementioned results.

show abstract

Section: Influence Of the Heating Rate In The Screensupporting

confidence: 73%

Examination and Evaluation of the Use of Screen Heaters for the Measurement of the High Temperature Pyrolysis Kinetics of Polyethene and Polypropene

Westerhout

Balk

Meijer

et al. 1997

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

show abstract

“…The second model was developed during this study to describe the pyrolysis kinetics on a more fundamental basis. This model incorporates a statistical reaction pathway model, which has successfully been applied to Bockhorn and Knü mann (1993) 200-600 0-50 1.1 8.3 × 10 19 310 c,b Cascaval (1970) 355-810 0 83 a,d 355-810 1 90 a,d Fuoss et al (1964) 394 1 5.0 × 10 24 323 d Jellinek (1950) 348-400 0 10 13.1 188 a,d,e Kishore et al (1976) 290-390 50-90 0 134 c,b Kokta et al (1973) 200-500 1 100-140 g 200-500 1 190-230 g Kuroki et al (1982) 310-390 1 1.8 × 10 11 152 b Madorsky (1953) 335-355 1 9.0 × 10 15 244 a Malhotra et al (1975) 180-390 1 189-440 b Mehmet and Roche (1976) 200-700 1 10 14.5 -10 15 219-229 a,i Mertens et al (1982) 500-800 1 92 c Risby et al (1982) Mw 100.000 g/mol 200-600 1 3.6 × 10 13 176 Mw 390.000 g/mol 200-600 1 6.1 × 10 12 165 Sato et al (1983) 100-600 0.75 3.5 × 10 11 177 b Wu et al (1993) 367-487 0.5 5.0 × 10 10 173 c this study 365-400 70-90 1 3.3 × 10 13 204…”

Section: Random Chain Dissociationmentioning

confidence: 99%

Kinetics of the Low-Temperature Pyrolysis of Polyethene, Polypropene, and Polystyrene Modeling, Experimental Determination, and Comparison with Literature Models and Data

Westerhout

Waanders

Kuipers

et al. 1997

Ind. Eng. Chem. Res.

299

176

View full text Add to dashboard Cite

The pyrolysis kinetics of low-density polyethylene, high-density polyethylene, polypropylene, and polystyrene has been studied at temperatures below 450°C. In addition, a literature review on the low-temperature pyrolysis of these polymers has been conducted and has revealed that the scatter in the reported kinetic data is significant, which is most probably due to the use of simple first-order kinetic models to interpret the experimental data. This model type is only applicable in a small conversion range, but was used by many authors over a much wider conversion range. In this investigation the pyrolysis kinetics of the forementioned polymers and a mixture of polymers has been studied at temperatures below 450°C by performing isothermal thermogravimetric analysis (TGA) experiments. The TGA experimental data was used to determine the kinetic parameters on the basis of a simple first-order model for high conversions (70-90%) and a model developed in the present study, termed the random chain dissociation (RCD) model, for the entire conversion range. The influence of important parameters, such as molecular weight, extent of branching and-scission on the pyrolysis kinetics was studied with the RCD model. This model was also used to calculate the primary product spectrum of the pyrolysis process. The effect of the extent of branching and the initial molecular weight on the pyrolysis process was also studied experimentally. The effect of the extent of branching was found to be quite significant, but the effect of the initial molecular weight was minor. These results were found to agree quite well with the predictions obtained from the RCD model. Finally, the behavior of mixtures of the aforementioned polymers was studied and it was found that the pyrolysis kinetics of the polymers in the mixture remains unaltered in comparison with the pyrolysis kinetics of the pure polymers.

show abstract

“…Figure 14 shows some of our results [24] and those of Malhorta et al [25] concerning the thermogravimetric behavior of anionic PS. However, in an earlier work on thermally polymerized PS [26] we observed an opposite dependence, but that time the calculations of the E,,, were performed by another method [27]. The dependence of the Eapp extrapolated of the degradation in air of the thermal polymerized PS for zero heating rate suggests random chain initiation and long "zip" (Fig 15).…”

mentioning

confidence: 81%

Some problems concerning the degradation of linear vinyl polymers and copolymers in nonisothermal conditions

Schneider¹

1978

J. polym. sci., C Polym. symp.

Self Cite

View full text Add to dashboard Cite

A critical review of the experimental results concerning the thermal degradation of linear vinylic polymers in dynamic conditions shows that generally the use of a single thermogravimetric curve may lead to ambiguous conclusions concerning both the steps and the mechanism of the thermal degradation, as well as the corresponding evaluated kinetic parameters. The ultimate values depend not only on the transformation degree, but also on the heating rate used, so that extrapolations may be recommended. However, the significance of the extrapolated kinetic parameters is still arguable, so that to compare thermogravimetric results, standard working conditions must be used. In such conditions the relative thermal stability of the polymers and the influence of comonomer units on the thermal behavior of copolymers may be appreciated.

show abstract

Über die kinetik des thermischen abbaues von polystyrolen

Cited by 15 publications

References 10 publications

Examination and Evaluation of the Use of Screen Heaters for the Measurement of the High Temperature Pyrolysis Kinetics of Polyethene and Polypropene

Examination and Evaluation of the Use of Screen Heaters for the Measurement of the High Temperature Pyrolysis Kinetics of Polyethene and Polypropene

Kinetics of the Low-Temperature Pyrolysis of Polyethene, Polypropene, and Polystyrene Modeling, Experimental Determination, and Comparison with Literature Models and Data

Some problems concerning the degradation of linear vinyl polymers and copolymers in nonisothermal conditions

Contact Info

Product

Resources

About